1. Field of Invention
The present invention relates generally to a method for improving the quality of printing processes involving black pixel depletion and, more specifically, to a method for printing composite ink in white spaces which are identified employing black pixel depletion data.
2. Description of the Related Art
A typical high quality color inkjet printer prints using at least four colors of ink: cyan, magenta, yellow, and black. A common black ink is a pigment-based ink where undissolved particles are suspended in a clear vehicle. Such pigment-based ink creates the darkest black with a minimum of bleed into the paper. Since the paper is typically white, any significant bleeding of the black ink into the paper will noticeably reduce the sharpness of the edges of black text or other black graphics.
For non-black color inks, dye-based inks are very popular. Dye-based inks do not have color particles suspended in solution and thus tend to bleed into the paper more than pigment-based inks. Since the dye-based ink wicks or bleeds into the paper, the dye-based inks dry faster than the pigment-based inks, which effectively pool on the paper surface. Non-black color inks may also be pigment-based.
In order to reduce ink dry time and/or decrease ink usage, xe2x80x9cblack pixel depletionxe2x80x9d processes (to reduce the density consistency of black text and objects) have been employed in thermal inkjet printersxe2x80x94within Hewlett-Packard Thermal Inkjet Technology (HP TIJ) single-pass print modes (in which the pen swaths are not overlapped), depletion masks have been used to identify black pixels targeted for depletion. See, e.g., U.S. Pat. No. 5,706,414 to Pritchard, incorporated herein by reference. With this black pixel depletion, however, there can be observable white pixels, especially if the drop size of the black pen is small, or if the media dot gain is small. Moreover, depletion masks are often arbitrarily matched with under/overprinting (UOP) maps (which are employed for speeding up the drying time of ink or improving its adhesion to a medium). See, e.g., U.S. Pat. No. 6,132,021 to Smith et al., incorporated herein by reference. With this arbitrary matching of the locations of black pixels with UOP pixels, xe2x80x9cwhite spacesxe2x80x9d which tend to detract from the print quality of black area fills can still be present. Accordingly, there is a need for a printing method which improves the print quality of printing processes involving black pixel depletion.
The printing method of the present invention generally involves printing composite ink in pixel spaces where a black pixel depletion process leaves unfilled pixel spaces. Black pixel depletion data are employed (the depletion mask is inverted) to generate a composite printing mask which designates pixel spaces which are candidates for being filled in with a composite ink. In a preferred embodiment, edge pixels of black fill areas are excluded from the candidate pixels. In a preferred embodiment, the white pixel spaces are filled in by printing a plurality of different colored inks (e.g., cyan/magenta/yellow or cyan/magenta) within these unfilled pixel spaces. In a preferred embodiment, the composite printing mask additionally serves as a UOP map.
A method for printing, in accordance with one embodiment of the present invention, includes the steps of: employing pixel depletion data to identify pixel locations; and applying composite ink to a piece of media at the pixel locations. The pixel depletion data are determined, for example, from a depletion mask (or table). According to a preferred method, the pixel locations are determined by inverting a depletion table. According to a preferred method, the pixel locations exclude edge pixel locations. According to a preferred method, the step of applying composite ink comprises sequentially applying different colored inks at the pixel locations to form the composite ink (e.g., black composite ink, composite ink including at least one dye-based ink, composite ink including at least one pigment-based ink, cyan/magenta/yellow composite ink, cyan/magenta composite ink).
A method for printing, in accordance with another embodiment of the present invention, includes the steps of: identifying depleted pixels of a printing pixel-array; and applying a plurality of inks at each location on a piece of media which corresponds to a depleted pixel. According to a preferred method, a depletion mask is employed to identify the depleted pixels. According to a preferred method, the pixel locations are determined by inverting a depletion table. According to a preferred method, the plurality of inks (e.g., at least one dye-based ink, at least one pigment-based ink, a combination of cyan, magenta and yellow inks, a combination of cyan and magenta inks) is applied one at a time at each location which corresponds to a depleted pixel.
A method for printing (with a printer apparatus including at least one carriage-mounted ink cartridge and a controller, the at least one ink cartridge including a plurality of pens configured to eject a first colored ink and a second colored ink, which, in combination, form a composite ink), in accordance with another embodiment of the present invention, includes the steps of: employing the controller to identify pixel locations from pixel depletion data and control the plurality of pens to apply the first colored ink and the second colored ink to a piece of media at the pixel locations to form the composite ink at the pixel locations. The pixel depletion data are determined, for example, from a depletion mask (or table). According to a preferred method, the pixel locations are determined by inverting a depletion table. According to a preferred method, the pixel locations exclude edge pixel locations.
The above described and many other features and attendant advantages of the present invention will become apparent as the invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.